CNit Documentation

Welcome to the documentation for CNit (Carbon-Nitrogen Interactions in Terrestrial ecosystems), the coupled carbon-nitrogen cycle model for MAGICC (Model for the Assessment of Greenhouse Gas Induced Climate Change).

CNit logo

CNit is a process-based terrestrial biogeochemistry model that simulates the coupled dynamics of carbon and nitrogen cycles in terrestrial ecosystems. The model tracks carbon and nitrogen through plant, litter, soil, and mineral pools, with explicit representation of carbon-nitrogen feedbacks, environmental effects (CO₂ fertilization, temperature, land use change), and nitrogen limitation on carbon uptake.

Key Features:

  • Explicit carbon-nitrogen coupling with nitrogen limitation feedbacks

  • Four nitrogen pools (plant, litter, soil, mineral) and three carbon pools

  • Environmental modifiers: CO₂, temperature, land use, nitrogen availability

  • Separation of deforestation and afforestation for CDR scenarios

  • Annual timestep with sub-annual process representation

  • Computationally efficient for integrated assessment modeling

Quick Navigation

🔬 For Scientists

Understand the model’s scientific basis, processes, and when to use CNit.

→ Start with CNit Model Overview, then see published papers in References.

📚 For Model Users

Install CNit and run your first simulation.

→ See Quickstart Guide for installation and basic usage.

→ See Example for a complete example with code and outputs.

🛠️ For Developers

Contribute to CNit development.

→ See CNit Physics API for implementation details with scientific descriptions.

→ See Contributing for development setup and coding guidelines.

Understanding CNit

Learn about the model’s structure, processes, and scientific basis before installing.

Getting Started

New to CNit? Start here to understand the model and run your first simulation.

User Guide

Learn how to use CNit effectively with examples and best practices.

API Reference

Complete documentation of all classes, methods, and modules. The API documentation includes detailed scientific descriptions, equations, and implementation details.

Development

Contact

CNit is developed and maintained by Gang Tang.

Questions or feedback?

Interested in contributing or collaboration? Please get in touch!

License & Citation

CNit is released under the BSD 3-Clause License.

Copyright (c) 2026, Gang Tang and contributors.

See the LICENSE file for full details.

If you use CNit in your research, please cite our papers.

  • Tang, G., Nicholls, Z., Norton, A., Zaehle, S., and Meinshausen, M.: Synthesizing global carbon–nitrogen coupling effects – the MAGICC coupled carbon–nitrogen cycle model v1.0, Geosci. Model Dev., 18, 2193–2230, https://doi.org/10.5194/gmd-18-2193-2025, 2025.

  • Tang, G., Zaehle, S., Nicholls, Z., Norton, A., Ziehn, T., & Meinshausen, M. (2026). Understanding the drivers of carbon–nitrogen cycle variability in CMIP6 ESMs with MAGICC CNit v2.0: Model and calibration updates. Journal of Advances in Modeling Earth Systems, 18, e2025MS005270. https://doi.org/10.1029/2025MS005270

Indices and Tables